In recent years, the development of thin-film silicon photoelectric conversion devices including amorphous silicon and crystalline silicon is actively performed. In the development of the photoelectric conversion devices, there are two particularly important points. One is a reduction in costs and the other is improvement of performance. The thin-film silicon photoelectric conversion device is characterized in that the photoelectric conversion layer thereof is thin compared with a crystalline silicon photoelectric conversion device in which a bulk body of monocrystal or polycrystal is used as a photoelectric conversion layer. Specifically, whereas the photoelectric conversion layer of the crystalline silicon photoelectric conversion device has thickness of several hundred microns, the thin-film silicon photoelectric conversion device has thickness of several microns. As a result, the thin-film silicon photoelectric conversion device has an advantage that raw materials necessary for forming the device can be reduced compared with the crystalline silicon photoelectric conversion device. On the other hand, efficiency of use of incident light is low compared with the crystalline silicon photoelectric conversion device. Therefore, the efficiency of use is increased using a light trapping technology.
The light trapping technology is a technology for forming a fine unevenness structure in a light incident section or a light reflecting section and capturing light into the photoelectric conversion layer. When light is made incident on the unevenness structure, a course of the light is refracted on an interface. Therefore, optical path length in the photoelectric conversion layer increases. Further, because total reflection on the interface is repeated, efficiency of use of the light increases.
Therefore, in the past, various light trapping technologies for using a transparent conductive film having a surface texture structure as an electrode of a photoelectric conversion device are proposed. For example, a technology for forming a large surface texture structure after etching by increasing crystal orientation of the transparent conductive film from a layer distant from a substrate to a layer close to the substrate is proposed (see, for example, Patent Literature 1). Further, a technology for forming, immediately on a first transparent conductive film, an average height difference of unevenness of the surface of which is 100 nanometers to 1,000 nanometers, a second transparent conductive film having average film thickness of 50 nanometers to 500 nanometers and having an average height difference of unevenness of the surface smaller than that of the first transparent conductive film is proposed (see, for example, Patent Literature 2).